1. Field of the Invention
The present invention relates to a method of setting a focus condition at the time of exposure, an apparatus for setting a focus conditions at the time of exposure, a program, and a computer readable recording medium.
2. Description of the Related Art
In a photolithography process in a manufacturing process of a semiconductor device, a plurality of processing and treatments are sequentially performed, for example, resist coating treatment in which a resist film is formed by applying a resist solution onto a wafer surface; exposure processing in which light in a predetermined pattern is applied to the resist film on the wafer to thereby expose the wafer to the light; heat-processing after the exposure which promotes chemical reaction in the resist film (post-exposure baking); developing treatment in which the exposed resist film is selectively dissolved with a developing solution, and so on, so that a predetermined pattern is formed in the resist film on the wafer.
Incidentally, it is necessary to form, on the wafer, the resist pattern with line widths having a uniform predetermined dimension within the wafer. Further, the line width of the resist pattern is greatly affected by exposure conditions such as the exposure amount, focus, and so on at the time of exposure processing in the photolithography process. Hence, it has been conventionally performed that the line width of the resist pattern formed on the wafer has been measured and the focus condition at the time of exposure has been set based on the measurement result (Japanese Translated National Publication of Patent Application No. 2001-534652 and Japanese Patent Application Laid-open No. 2003-86497).
In the aforementioned line width measurement, however, it is necessary to use a so-called electronic CD-SEM (Scanning electron microscope) which measures the line width by applying electron beams to the wafer. In this case, a large quantity of electrons collide against the wafer and may damage, for example, the resist pattern on the wafer. Therefore, the sufficient accuracy of the line width measurement is not ensured, causing difficulties to ensure the sufficient accuracy for the setting of the exposure conditions performed based on the result of the line width measurement. In addition, the line width measurement by the CD-SEM suffers from a disadvantage of consuming much time.
Besides, causes of variations in the line width of the resist pattern within the wafer include a variation component resulting from the exposure amount (dose of light) and a variation component resulting from focus at the time of exposure. The setting of the focus condition at the time of exposure has been conventionally performed based on the measurement result of the line width including both of the components, and therefore the setting has not been accurately performed. Therefore, the sufficient uniformity of the line width within the wafer cannot be secured.